The invention relates to a dispersion having an insecticidal action, a process for its preparation and its use.
DE 3835592 discloses the use of hydrophobic SiO2 for combating, for example, sucking insects. Such materials are applied by dusting on.
However, because of the dust nuisance (industrial hygiene) during application of these materials, this procedure is finding ever less acceptance by the user. The aqueous dispersions comprising only a hydrophobic silica and water which are also described in DE 3835592, however, do not show an adequate stability.
U.S. Pat. No. 5,830,512 describes a dispersion in which an adequate stability is achieved by addition of hydrophilic substances, such as, for example, silicas. However, the active hydrophobic component is diluted by a hydrophilic substance as a result of this. Furthermore, only a very low stability of the dispersion of hours to a few days is achieved.
It is known from EP 1 250 048 to stabilize the dispersion of hydrophobic silicon dioxide by gelling additives, such as xanthan gum, sodium alginates or neutralized carboxyvinyl polymers, mixtures of these additives also being possible.
In interplay with the hydrophobic SiO2 particles and incorporated air, these gelling additives moreover have the effect of a significant structural viscosity.
A pronounced structural viscosity offers advantages in application by spraying on: During the spraying process, the viscosity of the dispersion under the shear forces acting on it is relatively low. After the drops of dispersion have impinged on the surface to be covered, the viscosity rises again sharply, so that dripping/running off from perpendicular surfaces in particular is avoided.
The essential feature according to EP 1 250 048 is that in addition to the hydrophobic SiO2 particles to be dispersed, large amounts of air are also incorporated. In conventional dispersing processes, this cannot be avoided without the use of wetting surfactants and defoamers. Thus, a density of only 0.6 g/l is stated in Example 1. Approximately 40% of the volume is therefore air.
To achieve an adequate activity, a minimum mass must be applied to the surfaces to be sprayed. If only approximately 60% of the volume of the spraying equipment can be made use of per spraying operation, this means a significantly reduced efficiency of the staff performing the application.
The transportation and packaging costs and the disposal costs of the packaging required are adversely higher by this proportion.
An approximately 40% larger storage area must also be taken into account during storage.
Furthermore, a homogeneous, bubble-free covering of surfaces to be treated cannot be achieved with a dispersion containing air.